NCERT Class VII Science Solutions: Chapter 8-Winds, Storms and Cyclones Part 4

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Question 18:

When strong/high speed wind blows, an umbrella held upright at times gets upturned. Explain the reason.

Answer:

High speed wind passing over the umbrella creates low pressure. Therefore the umbrella upturns.

Question 19:

Suggest some precautions to be taken to prevent the roof of a tin sheet from flying away during a fierce wind storm.

Answer:

  1. Put heavy stones on it.

  2. Screw it tight.

LONG ANSWER QUESTIONS

Question 20:

Describe an activity to demonstrate that warm air is lighter than cool air.

Answer:

  1. Take two paper bags of the same size.

  2. Hang the two bags in the inverted position on the two ends of a wooden stick.

  3. Tie a piece of thread in the middle of stick and hold the stick by the thread in balance, as shown in the figure (A).

  4. Place a burning candle below one of the bags as shown in figure (B).

  5. You will observe that the balance of the bags is disturbed.

    Bags on balance

    Bags on Balance

    Bags on balance

    This activity indicates that as the warm air rises up it pushes the bag above the candle. This is because on heating, air expands and occupies more space. When same thing occupies more space, it becomes lighter. Thus, we can conclude that warm air is lighter than cool air.

Question 21:

The picture in Figure shows tree line along the sea coast on an island near the equator. As shown, the tree tops are permanently bent in one direction. Are the trees bent towards the sea or away from it? Explain.

As showing in images is a picture in Figure shows tree

The Picture in Figure Shows Tree

As showing in images is a picture in Figure shows tree

Answer:

In the day time wind blows from sea to land. This sea breeze makes the trees to bend towards the land.